José Luis León de la Luz1 y Alfonso Medel-Narváez

ABSTRACT

A new taxon of Asteraceae, Bidens cabopulmensis, from the Cape Region of Baja California Sur, is described and illustrated. It occurs on coastal sand dunes. The novelty is not especially close to the other eight known species of Bidens from the geographical area and differs by its habitat, life form, and details of the heads. It shares some characteristics with the mainland species, B. cronquistii, B. hintonii, and B. triplinervia. A key to identify the nine known species of Bidens native in the Cape Region is provided.

The Baja California Peninsula in northwestern Mexico and its adjacent islands (both Gulf and Pacific) constitute a natural region that has been the interest of numerous naturalists and biologists since the mid-nineteenth century. It is one of the largest peninsulas in the world (1400 km long, 40 to 200 km wide), extending southeast-northwest and having almost 4000 km of coastal environments, where geographical isolation from the mainland has been an important factor contributing to its current biotic composition.

The flora of the Baja California Peninsula has been compiled in two monumental treatments: Shreve and Wiggins’ Vegetation and Flora of the Sonoran Desert (1964) and Wiggins’ Flora of Baja California (1980). In the latter, 2958 taxa of vascular plants (including 686 endemics) are recognized. Rebman (2001) estimated the current plant biodiversity likely consists of approximately 4000 plant species, 30% of which are endemics. Furthermore, there remain poorly collected areas, where surveys are certain to yield many additional novelties, as in the present contribution.

In 2010, the Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (CONABIO) provided us funding for a project to explore coastal environments of the state of Baja California Sur. During our explorations in the east Cape Region, we collected two interesting specimens from the same geographic area, one of them belonging to the genus Bidens, that led to this paper.

First, using the Shreve and Wiggins’ (1964) flora, this specimen was compared with B. ferulifolia (Jacq.) DC. and the Baja California Cape Region endemic B. xanti (A. Gray) B.L. Turner because of the general characteristics of the flowers. However, both taxa were quickly rejected because they inhabit inland environments, such as the oak-pine woodlands of mainland Mexico and the scrublands of the Cape Region, respectively, and are of annual habit.

After collecting and analyzing mature fruits, we concluded that this specimen represents a new species of Bidens, based on characteristics such as dimorphic achenes, the peripheral one being incurved and the inner ones being clavate and graded in size. These features are coupled with a perennial habit and the fact that the known population only grows on stabilized coastal dunes, which seems to be its exclusive niche. We consider the population as a new micro-endemic species in the Cape Region.

Bidens cabopulmensis is distinct from the previously known Bidens species in the Cape Region and even in the Baja California Peninsula, and is not accounted for by previous workers in the area. The achenes of the ray florets, which possess markedly incurved corky margins (Fig. 2c), are especially noteworthy. They are superficially similar to those found in the genus Coreocarpus. In Melchert´s treatment (2010) of Bidens in Mexico this taxon will key to either B. cronquistii (Coreocarpus c. Sherff), B. hintonii (Coreocarpus h. Sherff) and B. triplinervia Kunth (B. canescens Bertol.), due to the dimorphic achenes where at least one type has corky wings, although the semi-succulent roots, growth habit, glabrescent character, and fine characters of the fruiting head are some particularities of B. cabopulmensis.

Another Mexican species that inhabits coastal dunes and nearby inland areas (1-10 m) along the Gulf of Mexico states is B. alba (L.) DC.var. alba,but is easily distinguishable by its prostrate robust habit, white rays, thick, and ample and undivided glabrous leaves (Ballard, 1986).

As circumscribed by Crawford et al. (2009), Bidens is a cosmopolitan genus of the tribe Coreopsidae represented by approximately 340 species and subspecific categories, of which about 56 occur in Mexico. Formerly and according to Villaseñor (1991), Bidens belongs to the tribe Heliantheae, one of the more diversified taxa of Asteraceae in Mexico, where approximately 65% are endemics. Also, the account of Mexican species of Heliantheae and its endemism show that the Baja California Peninsula is the natural region with the highest level. Additionally, plotting geographical distribution of the endemic peninsular Heliantheae, a clear tendency toward the southern tip is manifested.

A dichotomous key is provided below to differentiate B. cabopulmensis from the other eight taxa of Bidens previously recognized in the Cape Region, this largely abstracted from Melchert (2010) as follows:

Distribution and ecology. The novelty occurs on stable dunes in the vicinity of Punta Arena del Sur or “El Faro de Punta Colorada”, in a relatively small area between 23.563373° and 23.517585° N and -109.487397° and -109.469452° W, and occasionally in the proximities, occupying a total surface area of approximately 200 hectares. Plant density is estimated at one individual per 100-200 m2.

Phenology. Flowering usually extends from July through December.

Etymology. The taxon is named for the village of Cabo Pulmo, an eco-touristic settlement near one of the few coral reefs along the American Pacific coast and now seriously menaced by touristic developments along the east Cape Region.

ACKNOWLEDGEMENTS

We thank Thomas Melchert and Billie L. Turner for reviewing the article and providing helpful comments, as well as Reymundo Domínguez and Miguel Domínguez for assisting with fieldwork. Ira Fogel of Centro de Investigaciones Biológicas del Noroeste (CIBNOR) provided editorial services. Dr. Fernando Chiang helped us with the latin diagnosis. Also, two anonymous reviewers of this journal improved the original manuscript. This work was made possible with funds from Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (grant HJ-007 to Ileana Espejel), for which we are grateful.